Strong evidence has indicated that cerebral blood vessels from several species receive nonadrenergic, noncholinergic (NANC) vasodilator nerves. The nature of their transmitter substances, however, has not been positively determined. Several neural peptides such as vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and peptide histidine isoleucine (PHI) are present in high concentrations in cerebral arteries. These peptides induce an endothelium-independent vasodilation which is associated with an enhanced vascular cAMP formation, and therefore have been suggested to be the potential transmitters for cerebral vasodilation. Thus, multiple transmitters from different sources appear to mediate the cerebral neurogenic vasodilation. This possibility is further supported by our recent findings that transmural nerve stimulation (TNS)-induced but also cGMP content. Activation of the soluble guanylate cyclase, however, plays a predominant role in the neurogenic vasodilation. The candidate transmitter for activating the cGMP pathway and its relationship with the neuronal peptides in cerebral neurogenic vasodilation remains unknown. the endothelium-mediated dilations in cerebral and peripheral blood vessels are well established. There is good evidence that the endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) or a NO-releasing substance, and that the precursor from which it is synthesized is L-arginine. EDRF or NO induces vasodilation by activating soluble guanylate cyclase, and its synthesis is blocked by arginine analogues. In isolated cerebral arteries, we have demonstrated that the TNS-induced vasodilation was nearly abolished by a potent NO synthesis inhibitor. The inhibition was completely reversed by L-arginine but no D-arginine. It is hypothesized that NO or a NO- releasing substance mediates a major component of the NANC neurogenic vasodilation in the cerebral artery. The exact transmission mechanism of this dilator factor/NO has not been delineated. The proposed study continues to characterize the transmitter mechanism in cerebral NANC vasodilation. The in vitro tissue bath techniques, and techniques of biochemical and chemical analysis and morphology (immunohistochemistry) will be utilized to provide a comprehensive and multi-faceted approach to the problem. We plan to 1) examine formations of cyclic nucleotide and cyclic nucleotide protein kinase activities in isolated cerebral arteries without endothelial cells upon TNS, and applications of NO and vasodilating neural peptides (VIP, GCRP and PHI); 2) characterize the dilator responses in isolated cerebral arteries induced by TNS, and applications of NO and vasodilating peptides, and 3) examine the possibility that NO involved in cerebral neurogenic vasodilation can originate in the smooth muscle and the perivascular nerves. This research is a step toward our long-term goal to define the transmitter mechanisms in cerebral vasodilation and constriction, and their alterations in cerebral vascular diseases.